I am sorry but do you call the Siberian clip from JFK funny? It's not funny at all. It's scary.

For several reasons.

Obviously, there is a disoriented pilot with marginal English. Clearly, he has problems understanding the controller and probably finding his way around the airport.

On the other end, there is a controller who does not appreciate that fact at all. The controller wants to obtain the read-back without realizing that the mechanical read-back he is trying to impose on the pilot is NOT a guarantee of the comprehension of the instruction. The controller uses lots of unnecessary words ("sir", "I'm busy", etc.) that confuses the pilot even further.

I think we tend to forget that the bad communications were behind some of the deadliest accidents.

Isn't english supposed to be the primary language for air traffic control in the entire world, or just the united states?

English is indeed the primary language of ATC for the entire world, but in many countries/locations, more than just english is spoken if both the ATC and pilot speak the other language. (ie: Montreal [French], Mexico [spanish])

It gets confusing for other english-only speaking pilots on the freq. because you then do not know where the aircraft speaking the other language is in relation to your position.